how did roger chillingworth and mr.dimmesdale become such good freinds?

Actually their relationship was as dysfunctional as you can get. They were roomates of sorts under the guise of Chillingworth helping Dimmesdale get better from his vatrious stress related sicknesses. Chillingworth was a doctor of some sort. In reality he was slowly killing Dimmesdale and messing with his mind. So, calling it friendship would sort of be a too much.